The present invention relates to a medical system, a method of using the system, and a hollow X-ray tube unit catheter according to the preambles of the independent claims.
In general the present invention relates to connecting a miniature X-ray tube for in vivo use to an electrical power source. A miniature X-ray tube according to the invention is, for example, useful in applications for prevention of restenosis and for treating diseases, such as cancer, in a living body.
In treating stenosis in coronary arteries, a restenosis occurs in 30-60% of the cases. It is known that a treatment with beta- or gamma- (X-ray) radiation will decrease the occurrence of restenosis substantially.
Another example of an application of the present invention is treatment of cancer tumors where it is desired to deliver radiation locally.
Methods to apply the radiation to the site of treatment are presently subject to intensive research. Generally, a hollow catheter is inserted into the body, typically via an artery, in such a way that its distal end is placed near the site of treatment. A source of radiation attached to the distal end of an elongated member is inserted into the hollow catheter, and is forwarded until the radiation source is disposed at a proper position for radiating the site of treatment. In the specific case of treating cardiac vessels, the catheter is placed near the cardiac vessel tree (this catheter often called a xe2x80x9cguide catheterxe2x80x9d). A very thin wirexe2x80x94called guide wirexe2x80x94is then used to probe further and reach the site where treatment shall be performed. The therapeutic device is moved along this wire, i.e. by threading the device onto the guide wire. It is obvious that the therapeutic device has to have a hole close to its distal end in order to do this. Radiation treatment methods using radioactive pellets, wires or balloons etc. as radiation source is known in the art. Since these methods have some drawbacks, such as the need for substantial efforts to control radiation in the environment outside the patient, the use of a nature electrical X-ray tube including a cold cathode has been proposed. Such a tube may be switched on and off due to its electrical activation. An example of such an X-ray tube is described in the U.S. Pat. No. 5,854,822 as well as in U.S. Pat. No. 5,984,853.
A conventional miniature electrical X-ray tube requires electrical conductors to connect the tube, i.e. its anode and cathode, to an external power supply. Conventionally, two conductors, one for the cathode and one for the anode of the tube are connected to the tube, preferably, and as known from prior art in a coaxial arrangement. FIG. 1 schematically illustrates an X-ray tube according to this prior art. However, due to the small dimensions used, the outer diameter of the connecting cable is typically in the range of 1-5 mm when used for cancer treatment and less than 2.0 mm when used in cardiology, and the high voltages used, typically 20 kV, the probability for electrical breakdown between the connections to the tube is considerable. The European Patent application No. 00850173.6, filed Oct. 24, 2000, by the same applicant as the present application, relates to a medical device that is directed to solve that problem. Principally and in short the problem is solved by connecting the proximal pole of the X-ray tube to the external power source via an electrical conductor integrated in the elongated X-ray tube unit that is inserted into an X-ray tube unit catheter. The distal pole of the X-ray tube is connected to an electrical connection arranged at the inner surface of the vertical distal end of the catheter. The electrical connection is then connected to the external power source via an electrical conductor integrated into the wall of the catheter.
It has not been widely recognized to date the importance to center the X-ray source in the cardiac vessel during the radiation treatment. The electrical X-ray source emits a spectrum of radiation in the range of 8-20 kV (for a 20 kV driven device). The lower energies will not penetrate as far into the tissue as the higher energies. Also, even the higher energies have a clear dose fall-off in the tissue of interest. It has recently been found that an optimal target dose of about 16 Gy should be delivered 0.7 mmn into the vessel wall for to achieve the best clinical results. The comparatively rapid dose fall off is also an advantage, because the amount of radiation delivered to healthy tissue further away from the source of ionizing radiation is reduced, as compared to for instance Gamma emitting sources such as Ir-192.
Not centering the soft X-ray emitter may result in too low radiation dose delivered to the part of the vessel wall that is farthest away from the source and too high doses delivered to the tissue that is closest to the wall. FIG. 5 shows the calculated radiation profile in the walls of a 3 mm vessel where the source of ionizing is placed in direct contact to the wall and in the center respectively. As can be seen the farthest wall receives too low doses, and the wall in contact receives too high doses.
In addition to the above, an electrically activated X-ray device can essentially be regarded as a point source. Since the treated site is usually longer than the approximately 1 mm length such a device will cover, the device must be pulled back during the treatment.
U.S. Pat. No. 6,148,061 is primarily directed to a miniature X-ray unit provided with an X-ray transmission window through which X-rays exits the unit. It is also briefly discussed that if the radiation dose must be delivered to a portion of an artery longer than the length of the X-ray window, the unit must be moved while in the activated state along the artery lumen. This can be accomplished by feeding the X-ray unit into, or out of, the guide catheter at the insertion location. The X-ray unit is preferably moved along the length of the treatment region under computer control to insure the correct X-ray dose is delivered to each location along the artery. After treatment, the unit is turned off and removed from the guide catheter.
The benefit of centering the catheter in a vessel is shortly commented in U.S. Pat. No. 6,148,061 where the X-ray unit is centered in an artery to achieve uniform dose delivery around the inner wall of the artery. The X-ray unit can be centered by providing a centering balloon or other inflatable device around the X-ray unit.
U.S. Pat. No. 6,095,966 describes an X-ray device for delivering localized radiation to an interior of a body. The device includes an inflatable balloon arranged around the X-ray emitter to provide a cooling solution to cool the X-ray emitter and dissipate the potentially damaging heat. This known device is positioned at the treatment position by means of the inflated balloon. The device is particularly suited to esophageal applications where it is not so crucial to temporarily block the lumen as in blood vessels.
One object of the present invention is to achieve a medical system adapted to perform treatment at treatment sites having a length of several mm and at the same time achieving a high security with regard to avoiding electrical breakdown between the connections to the tube.
One further object of the present invention is to achieve a medical system where the generated X-ray radiation is conformably applied at a treatment position in a blood vessel and where blood may pass the X-ray tube catheter during the treatment.
The above-mentioned objects are obtained by a medical system, an elongated X-ray tube unit catheter and also by a method of using the medical system according to the characterizing portions of the independent claims.
Preferred embodiments are set forth in the dependent claims.
According to one preferred embodiment of the present invention one of the conductors for supplying voltage to the X-ray tube is integrated with, or attached to, the hollow catheter used to provide a path for inserting the X-ray source. At the distal end of the hollow catheter, said conductor is exposed at the inside of the hollow catheter to exhibit a terminal surface. The electrical connection to the X-ray tube is at one end (the proximal end when inserted into the hollow catheter) connected to a single electric cable, while the other end (the distal end when inserted into the hollow catheter) is provided with a terminal end surface adapted to achieve an electrical connection to the inner surface along a predetermined length of the hollow catheter when inserted into said catheter.
Another great advantage is that the X-ray tube unit with the radiation source need not be sterilized because it is inserted into the hollow catheter that has an open proximal end to receive the tube unit and a closed distal end. Therefore only the catheter needs to be sterilized in that the X-ray tube unit is never in contact with body tissue. Thus, the X-ray tube unit itself may be reused without sterilization. This should be compared with prior art systems where the insertion catheter (or guide catheter) has an open distal end and where the radiation source unit is in contact with body tissue.
A thirs great advantage of the present invention is that, if, due to unforeseeable circumstances any part of or the whole X-ray tube is damaged in any way, no parts would be spread inside the body but would instead be kept inside the hollow catheter.
The catheter further is improved in order to center the catheter in a vessel while still allowing blood flowxe2x80x94at least partlyxe2x80x94to pass the device. This is an important aspect in order to supply blood to the parts of the tissue that obtain their blood supply distally from the device.
A fourth advantage of the present invention according a preferred embodiment is that the dosimetry, i.e. the control of the dose delivered to the tissue is greatly enhanced.
A fifth great advantage is that the catheter will help heat transfer, since the electrically conducting layer described in more detail below, also will aid the heat flux from the tube to be distributed away from the source. The plastic further helps as a thermal isolator.